Radar resource utilization is a high priority in military radars. Radar is used to scan for new threats as well as to keep track of already identified threats. Conserving radar resource utilization in one application can free up the radar for other applications.
Simultaneous tracking of multiple targets has been implemented in primarily four ways in the past: 1) tracking one target for a single pulse or dwell and then quickly switching to one or more additional targets; 2) beamspoiling on transmit and forming multiple receive beams; 3) partitioning the array faces into different subapertures and then forming a different transmit beam out of each subaperture; and 4) shotgunning, which is transmitting different pulses to multiple targets and then simultaneously receiving pulses back from all targets. Method one results in high track resource utilization, which limits the number of other operations (such as search) that can be scheduled for a radar. Method 2 can be effective for searching a large volume, but beamspoiling the transmit beam results in a large amount of wasted energy being sent to angles where targets are not present. Method three uses lower power and lower gain, resulting in decreased sensitivity and decreased angular resolution. Finally, while the shotgunning method is sometimes effective, on its own it may not be effective if the radar is not able to quickly switch from transmitting one pulse to the next.
FIG. 1 shows a typical prior art radar approach used to track targets. The radar 10 emits a transmit beam with a main lobe 20 aimed at primary target 15 and sidelobes 25. The sidelobes 25 are all of the lobes other than the main lobe, and are effectively wasted energy, as the prior art method requires a separate main lobe to be aimed at the secondary target in order for the secondary target 30 to be tracked. The use of a new main lobe for each target consumes significant radar resources, and each new main lobe has associated wasted sidelobe energy that is not utilized.
FIG. 2 shows another typical prior art radar method used to track targets. In this prior art embodiment, beamspoiling is used to cause the radar 10 to effect a wide transmit beam pattern 50. Individual receive beams 55 may be digitally formed in the direction of known targets. The wide transmit beam pattern can detect a primary target 15 as well as secondary targets 30, but significant radar resources are wasted because the wide transmit beam sends energy in all directions regardless of where the targets are. In addition, as is known in the art, beamspoiling results in a loss of gain, therefore longer dwell times are needed using this prior art method.
Thus, a system and method is needed for tracking multiple targets that reduces radar resource utilization, that wastes less energy by minimizing transmit beams to angles where there are no targets, which has acceptable sensitivity and angular resolution, and which is usable in a variety of situations.